SOLUTION

Intermittent periodic duty with starting:- The intermittent periodic duty with starting consists of the sequence of identical duty cycles each comprising a period of starting, a period of operation of constant load followed by a rest period. The operating and rest periods of the motor are short to attain the thermal equilibrium during one duty cycle.

In Intermittent periodic duty with starting the stopping of the motor, is obtained by natural deceleration after disconnecting the electric supply by means of mechanical brake which does not cause additional heating of the windings.

This type of duty is characterized by the cyclic duration factor, the number of duty cycles factor of inertia which is the ratio of the combined inertia of the motor and load to the motor inertia.

Cyclic Duration = (D + N) ⁄ (D + N + R)

Where D = starting time
N = Operation time under rated load
R = time for rest

The factor of Inertia = (Inertia of load + Inertia of motor) ⁄ (Inertia of Motor)

Examples:- Motors that drive metal cutting lathes and certain auxiliary equipment of rolling mills are subjected to such operating conditions.